Let's give it a #try

A frequent bit of code seen throughout applications looks like this:

shopping_cart && shopping_cart.items

Or another snippet including an if statement to verify the presence of a user:

name = nil

if user && user.profile
  name = user.profile.full_name
end

Even though this code looks quite minimal, Rails makes it even easier by providing a method called try. Here’s how it works:

shopping_cart.try(:items)

try only calls the items method if shopping_cart responds to items. If it’s nil, it doesn’t respond to the items method, and nil is returned. There’s also a try! method, which raises a NoMethodError if shopping_cart is not nil and does not respond to items.

Note that below Rails 4.0, try has the behaviour of try!, so it raises a NoMethodError if shopping_cart does not define the method being called.

The nice thing about try is that the nil object also implements this methods, which always returns nil. This means we can chain the try method to make things a lot easier! Take a look at how we can radically reduce the second example:

name = user.try(:profile).try(:full_name)

Nice. It makes the code more readable. Arguments can easily be passed along with the call to try:

product.try(:price, currency)

Do make sure you pass the correct number of arguments. Otherwise you’ll get an ArgumentError, try won’t be handling this for you.

If you pass a block to try, the block is passed along to the method being called:

pictures.try(:each) do |picture|
  print(picture)
end

If pictures is nil, the tried method isn’t called, and therefore the block won’t be called either.

In a nutshell, this is what try does. It’s also well documented on the Rails documentation website.